Field of the Invention
The present invention relates to electrosurgical systems and methods, and more particularly, electrosurgical systems and methods using argon plasma during cutting modes of operation.
Brief Description of the Related Art
The standard means for controlling traumatic and surgical blood loss are electrosurgical generators and lasers which respectively direct high-frequency electrical currents or light energy to localize heat in bleeding vessels so as to coagulate the overlying blood and vessel walls. Hemostasis and tissue destruction are of critical importance when removing abnormal tissue during surgery and therapeutic endoscopy. For monopolar electrosurgery electrical energy originates from an electrosurgical generator and is applied to target tissue via an active electrode that typically has a small cross-sectional surface-area to concentrate electrical energy at the surgical site. An inactive return electrode or patient plate that is large relative to the active electrode contacts the patient at a location remote from the surgical site to complete and electrical circuit through the tissue. For bipolar electrosurgery, a pair of active electrodes are used and electrical energy flows directly through the tissue between the two active electrodes.
U.S. Pat. No. 4,429,694 to McGreevy disclosed a variety of different electrosurgical effects that can be achieved depending primarily on the characteristics of the electrical energy delivered from the electrosurgical generator. The electrosurgical effects included pure cutting effect, a combined cutting and hemostasis effect, a fulguration effect and a desiccation effect. Fulguration and desiccation sometimes are referred to collectively as coagulation.
A conventional desiccation procedure, shown in FIG. 1B, typically is performed by holding the active electrode in contact with the tissue. Radiofrequency (RF) current passes from the electrode directly into the tissue to produce heating of the tissue by electrical resistance heating. The heating effect destroys the tissue cells and produces an area of necrosis spreading radially from the point of contact between the electrode and the tissue. The necrosis is usually deep.
A conventional fulguration procedure, shown in FIG. 1A, may be obtained by varying the voltage and power applied by the electrosurgical generator. Conventional fulguration procedures typically were performed using a waveform which has a high peak voltage but a low duty cycle. If the active electrode was brought close to but not touching the tissue and the peak voltage was sufficient to produce an RF arc, fulguration would occur at the point where the arc contacted the tissue. Due to the low duty cycle, the power per unit time applied to the tissue was low enough so that cutting effects were minimized.
A conventional cutting procedure, shown in FIG. 1C, may be obtained by delivering sufficient power per unit time to the tissue to vaporize cell moisture. If the power applied is high enough a sufficient amount of steam is generated to form a steam layer between the active electrode and the tissue. When the steam layer forms, a plasma consisting of highly ionized air and water molecules forms between the electrode and the tissue. An RF arc then develops in the plasma. At the location where the arc contacts the tissue, the power density becomes extremely high and instantaneously disrupts the tissue architecture. New steam is thereby produced to maintain the steam layer. If the power density is sufficient, enough cells are destroyed to cause a cutting action to occur. A repetitive voltage wave form, such as a sinusoid, delivers a continuous succession of arcs and produces a cut with very little necrosis and little hemostasis.
It also was possible to create a combined combination of effects by varying the electrical waveform applied to the tissue. Specifically, a combination of conventional cutting and desiccation could be produced by periodically interrupting the continuous sinusoidal voltage typically used to perform a conventional cutting procedure. If the interruption was sufficient, the ionized particles in the plasma between the electrode and the tissue would collapse, causing the electrode to momentarily come into contact with the tissue. That touching would desiccate the tissue thereby sealing off blood vessels in the vicinity of the electrode.
Conventional electrosurgical generators typically have both “cut” or cutting and “coag” or coagulation modes of operation. As previously noted, the cut mode typically will have a low voltage waveform form with a high duty cycle, e.g. 100%. The coag mode of an electrosurgical generator typically creates a waveform with large amplitude but short duration “spikes” to achieve hemostasis (coagulation). For example, in coag mode an electrosurgical generator may use a high voltage wave form at a 6% duty cycle. The surrounding tissue is heated when the waveform spikes and then cools down (between spikes), producing coagulation of the cells. Fulguration is achieved in the coag mode of the electrosurgical generator, with the tip of the surgical “active electrode” held above (but not in contact with) the tissue. Electrosurgical desiccation is achieved in either the cut or coag modes of the generator. The difference between desiccation and fulguration is the tip of the “active electrode” must contact the tissue as in FIG. 1B in order to achieve desiccation. Typically, the more desired mode to achieve tissue desiccation through direct tissue contact is the cut mode. Different degrees of hemostasis (coagulation) can be achieved by utilizing varying degrees of “Blended” waveforms, e.g., 50% on/50% off, 40% on/60% off, or 25% on/75% off.
Another method of monopolar electrosurgery via argon plasma technology was described by Morrison U.S. Pat. No. 4,040,426 in 1977 and McGreevy U.S. Pat. No. 4,781,175. This method, referred to as argon plasma coagulation (APC) or argon beam coagulation is a non-contact monopolar thermoablative method of electrocoagulation that has been widely used in surgery for the last twenty years. In general, APC involves supplying an ionizable gas such as argon past the active electrode to target tissue and conducting electrical energy to the target tissue in ionized pathways as non-arcing diffuse current. Canady described in U.S. Pat. No. 5,207,675 the development of APC via a flexible catheter that allowed the use of APC in endoscopy. These new methods allowed the surgeon, endoscopist to combine standard monopolar electrocautery with a plasma gas for coagulation of tissue.
APC has been demonstrated to be effective in the coagulation of blood vessels and human tissue during surgery. APC functions in a noncontact manner. The electrical current is initiated only when the tip of the handpiece or catheter is within one centimeter of the target tissue and produces a homogenous 1 mm to 2 mm well-delineated eschar. The eschar created by APC is further characterized by a decrease absence of charring and carbonization compare to eschar resulting from conventional electrosurgical fulguration. The eschar remains firmly attached to the tissue, in contrast to other coagulation modalities where there is an overlying charred layer of coagulated blood. There is minimal tissue necrosis with APC.
In U.S. Pat. Nos. 5,217,457 and 5,088,997 to Delahuerga et al. disclosed a device for performing procedure referred to as “argon shrouded cut.” The device was an electrosurgical pencil having an exposed electrode with a distal end defining a tip for cutting biological tissue and a nose piece mounted about the electrode to define a pathway for a stream of inert gas which shrouds the electrode at or near its tip. When in coagulation mode, a convergent stream of inert gas was directed directly onto the tip of the electrode. In coagulation mode, the voltage was sufficient to initiate an electrical discharge in the inert gas. In cut mode, the stream of ionized gas was directed to impinge obliquely on the electrode at a point adjacent to but away from the tip of the electrode. In cutting mode, the open circuit voltage was generally not high enough to continuously plasmatize the inert gas and initiate and maintain an electrical discharge. Accordingly, in cut mode the function of the inert gas is to provide a shroud around the electrode rather than to initiate electrical discharge.
A multitude of literature exists that discloses and discusses various commercially available electrosurgical generators and the voltage waveforms produced by those generators. For example, A. Erwine, “ESU-2000 Series Product Overview A Paradigm Shift in Electrosurdery Testing Technology and Capability Is Here,” BC Group International, Inc. (2007) describes electrosurgical generators from ERBE Elektromedizin GmbH and ConMed Corporation, among others.